Lighting Research & Technology

Consideration is being given to the adoption of a new metric characterizing light as it affects the human circadian system. Much has been learned over the past couple of decades about light as a stimulus for circadian system regulation, so it is appropriate that these discussions take place. The present paper develops an argument for adopting circadian stimulus as a metric for quantifying light in architectural spaces. The circadian stimulus metric (a) was developed from several lines of biophysical research, including those from basic retinal neurophysiology; (b) has been validated in several controlled experiments; and (c) has been used successfully in a number of real-world applications. Any discussions of new metrics should take each of these foundational points into consideration.

How we look at other people may affect conclusions drawn about the effect of changes in lighting when this task needs to be done after dark. This paper reports further analysis of the distance and duration of fixation on other pedestrians, updating a previous review by considering a greater number of fixations and by examining the influence on these of other characteristics such as the relative direction of travel. This analysis provides further support for a tendency to fixate others at a distance of 15 m and for a duration of 500 ms.

LED technology provides new opportunities to change the illuminance on pedestrian pathways in response to the presence of people. This study explores possible effects of dimming as such on walking, legibility and perception. In an indoor full-scale laboratory, 61 participants walked along a 19-m pathway with a motion-detection sensor 10 m before an LED luminaire. The participants walked significantly slower under dimmed than static lighting conditions, even after the illuminance had increased. Legibility decreased with the extent of dimming. The larger the difference in illuminance between dimmed and full light, the stronger the self-reported reaction. The results indicate that changes in illuminance affect walking, and that legibility and perception are affected by the overall lighting design of pedestrian pathways rather than by dimming as such.

An experiment was carried out to investigate how contrast threshold for target detection is affected by the presence of glare and by extraneous light sources using the method of ascending limits. The target was located at either a foveal or a peripheral (10° right) location, glare was adjacent to the foveal location, simulating the headlamps of an oncoming vehicle, and extraneous light sources were at either foveal or peripheral (10° right or left) locations. Contrast threshold for a foveal target without glare was affected mainly by the surrounding local luminance distribution. However, in the presence of glare and also for the peripheral target (both with and without glare) the global luminance distribution matters. Glare increased the contrast needed for detection of the foveal target, but this effect was reduced by the presence of extraneous light sources that were peripheral to the target. For peripheral targets, contrast threshold was also reduced by the presence of extraneous light at a non-target location and this effect was increased in the presence of glare. Glare equations tend to be based on tests using uniform, homogenous fields: these data indicate that, in the presence of extraneous light sources, the influence of glare is overestimated.

Flashing yellow warning lights are important for worker and driver safety in work zones. Current standards for these lights do not address whether and how they should be coordinated to provide directional information to drivers navigating through work zones. A field study was conducted to assess driver responses to warning lights. The luminous intensities and flash patterns of warning lights along a simulated work zone were varied during daytime and nighttime. During the daytime, driver responses were relatively insensitive to warning light characteristics, although drivers preferred sequential and synchronised flash patterns over random, uncoordinated flashing. At nighttime, the combination of a temporal peak luminous intensity of 25 cd and a sequential flash pattern was optimal for providing directional information. A single initial warning light having a higher luminous intensity may help drivers detect the work zone without creating unacceptable visual discomfort.

In this paper, the performance of a dynamic light controller (DLC) is experimentally evaluated to achieve a dynamic light source consisting of alternative arrays of warm white and cool white light-emitting diodes (LEDs). The DLC is programmed to drive the light source through both step and continuous variations of correlated colour temperature (CCT) and light output. For step variation, the DLC generates pulse width modulation (PWM) signals to drive the LED arrays to achieve 16 desired set points out of four CCTs (2900–5600 K) and four illuminances (100–300 Lux). The measured set points show deviations within acceptable limits. For continuous variation, the DLC is programmed to make the dynamic light source follow a time-varying pattern of CCT and Illuminance. The variations of measured values are mostly within acceptable limits except at lower CCT and illuminance points. The measured duty cycles of the generated PWM signals from the DLC are almost equal to the corresponding calculated values for both the step and continuous variations indicating good performance. The measured deviations are caused by the differences in lumen output at duty cycles <10% compared to the estimated values.

Various emerging technologies encourage the embedding of intelligent and climate responsive behaviour into architectural elements. Light-shelves have been used for decades to enhance natural light in spaces, however, their static nature is limiting their overall performance potential. This paper explores the convergence of rapid prototyping, parametric design and environmental modelling software to create a dynamic and direct-reflection daylight redirection system that significantly enhances daylight availability. A Radiance-based simulation workflow to optimise and study the system is used and a 1:1 mock-up is developed. The mock-up is based on a horizontal-light shelf with an array of mirror tiles that can tilt in two axes based on sun position. The potential impact of such a system is then evaluated for a side lit office space in multiple climates in the northern hemisphere. Results show that daylight can be redirected deep into the building more effectively and therefore improve daylight availability for otherwise underlit floor plan regions. Projected savings for electric lighting range from 17% to 35% compared with a static redirection system.

This paper describes an experiment for assessing the discomfort glare caused by light emitting diodes (LEDs) having different colours. The results showed that coloured LEDs induce more discomfort glare than a white LED. On comparing different coloured LEDs, blue ones gave the highest glare perception, especially for those having shorter peak wavelengths. Different earlier proposed luminous efficiency functions for discomfort glare were applied to re-define luminance. This led to modified unified glare ratings, which achieved very accurate predictions of the visual results. A modified brightness based on a colour appearance model for unrelated lights was used to predict glare and also performed very well.

Light pollution has a serious impact on astronomical observations and ecological balance. So far, most scholars have carried out field measurements of urban sky glow luminance using satellite data. However, measurement of the light environment of an entire city is insufficient. This paper presents measurements of the sky within the city of Dalian and examines the changes in the distribution of luminance and colour temperature of the sky. It was found that over the transition from day to night the colour temperature of the sky decreases by approximately 2000 K–3000 K and the light spectrum transforms from a relatively uniform distribution to one with an obvious peak. Additionally, the zenith luminance is up to 0.01 cd/m², more than 50 times the standard dark sky luminance. Dalian experiences serious light pollution.

Indoor lighting is facing a massive retrofit to LED lighting. Research is needed to assess whether LED-based lighting can promote energy efficiency, boost visual comfort and support biological functions. This field study considered the lighting of four identical classrooms in an upper secondary school in Helsingborg, Sweden. Two classrooms were fitted with state-of-the-art ceiling pendants containing T5 fluorescent tubes and that had a direct/indirect light distribution (the control rooms). The other two classrooms were fitted with an experimental LED indirect lighting system (the experimental rooms). In the classrooms, 72 students aged 17–18 years performed their usual educational activities over a whole academic year. The light environment, electricity consumption, and students’ mood, light perception and saliva cortisol concentration were monitored. The two lighting systems produced only marginal differences. Overall, the experimental rooms were slightly preferred but achieved only small energy savings due to high parasitic losses.